One-piece multipole plate for a magnetic holding apparatus, process for making such plate and magnetic apparatus using such plate

ABSTRACT

The present invention relates to a one-piece multipole plate for a magnetic clamping apparatus, a process for making such plate and a magnetic apparatus having such plate, wherein the magnetic apparatus has a plurality of pole pieces and said plurality of pole pieces extend from said plate and are formed of one piece with said plate.

The present invention relates to a one-piece multipole plate, preferablybut without limitation for a magnetic clamping apparatus and a processfor making such plate, as defined in the preambles of claims 1 and 12respectively.

As used herein, the term magnetic clamping apparatus is intended toindicate:

-   -   a permanent-magnet apparatus, i.e. an apparatus that does not        require any power supply when used for clamping or for changing        its state from active to inactive and vice versa, and is formed        with permanent magnets in appropriate arrangement within the        apparatus;    -   an electro-permanent apparatus, i.e. an apparatus that does not        require any power supply when used for clamping and requires        power supply when it is activated and inactivated, and is formed        with reversible permanent magnets and, if needed, with static        permanent magnets in appropriate arrangement within the        apparatus;    -   an electromagnetic apparatus, i.e. an apparatus that requires        power supply when used for clamping, whose magnetic core is made        of ferromagnetic material.

In prior art, also with reference to FIGS. 1A and 1B, the process formaking a magnetic clamping apparatus 1 for example of theelectro-permanent dual-magnet type, includes a first step in which aframe is formed from solid ferromagnetic material, in which a number “N”of coils 3, also known as solenoids, are arranged.

Otherwise, the frame 2 may be formed by assembling together variouscomponents with methods well known to those skilled in the art.

The solenoids 3 are appropriately arranged to obtain North/Southpolarities and are electrically, connected with a power source locatedoutside the frame 2 (not shown).

The solenoids 3 have such a configuration as to define a space forreceiving a reversible magnet 4, such as a magnet of the AlNiCo type,above which a pole piece 5 is placed.

The pole piece 5 is obtained by mechanically machining solidferromagnetic material.

It shall be noted that, as used herein, the term pole piece is intendedto indicate an element formed of ferromagnetic material that typicallyhas a surface that is magnetically neutral when the magnetic apparatusis not activated and magnetically active when the magnetic apparatus isactivated.

In the particular representation of FIG. 1B, the pole piece 5 is shownas a ferromagnetic element having a square plan section with six facesof given width, length and thickness.

Particularly, the pole piece 5 has four of its six faces in which themagnetic field is oriented in one direction, a fifth face in which thedirection of the magnetic field, and thus its North/South polarity, canbe changed, and a sixth face 5A that can be neutral when the magneticapparatus is not activated or have the same polarity as the remainingfive faces when the magnetic apparatus is activated.

It shall be noted that the magnetic apparatus 1 comprises a plurality ofpole pieces 5, which are physically separated from each other and arecoupled to the frame 2 to form a workpiece holding surface 2A, on whichthe workpieces to be mechanically machined are arranged.

In other words, all the faces 5A of the pole pieces 5 form the holdingsurface 2A of the magnetic plate of the magnetic apparatus, on which theworkpieces to be mechanically machined are arranged and firmly clamped,as the magnetic apparatus is activated.

Then, the process includes the step of associating the pole pieces 5with the frame 2, for example, by means of a screw 6, so that thesolenoid 3-reversible magnet 4 assembly can be clamped into a pack.

For this purpose, to allow each pole piece 5 to be coupled to the frame2, holes 7 are formed both in the frame 2 and in the pole piece 5, suchholes being designed to engage the screw 6 for clamping each pole piece5 against the frame 2.

Furthermore, pole extensions (not shown) may be respectively associatedwith one or more pole pieces 5, when specifically needed for machiningthe workpieces.

The pole extension may be associated with the pole piece 5 of themagnetic apparatus 1, for example, by screw connection of the poleextension in an additional hole 8 formed in the pole piece 5, such hole8 extending along the same longitudinal axis of the hole 7.

Also, the process includes a step during which a static magnet 9, suchas Ferrite or NdFeB, also appropriately oriented, is fitted in the gapbetween the pole pieces 5.

Finally, the process includes a “calibration” step, in which the flux ofthe reversible magnet 4 is balanced with the flux of the static magnet 9and a resin casting step 10, whereby the magnetic apparatus 1 can bemade substantially impervious to impurities and/or liquid infiltrations,and any gaps can be filled.

Nonetheless, this process for making the apparatus 1 still suffers fromcertain problems, including the ones associated with the calibrationstep.

In addition to being time consuming, the calibration step has to becarried out by specially skilled persons.

It shall be noted that the calibration step is required due to certainproblems specially associated with the magnetic apparatus 1, such as:

a) the total flux value that can be obtained from the static magnets ofeach pole piece, even when it is statistically calculated beforehand,may differ from the value of the reversible magnet being used, in termsof quality, quantity, etc.;

b) the center-to-center distances between each pair of pole pieces 5that form the holding surface of the magnetic, plate, as well as thedistances between the faces of each pair of pole pieces 5 can change dueto dimensional tolerances of the various materials (static magnet, polepieces);

c) the faces of each pair of pole pieces 5 between which the staticmagnet 9 is fitted are non-parallel due to the screw connection of thepole piece with the frame.

In addition to the above, more problems are associated with thefabrication of a magnetic apparatus, whether or not it is ofelectro-permanent dual-magnet type, such as:

-   -   the impossibility of achieving accurate alignment and equal        spacing of the holes 8 formed in the top of the pole pieces 5;    -   the poor ability of pole pieces 5 of absorbing the vibrations        caused by mechanical machining of workpieces held against the        clamping plate, particularly when pole extensions are used;    -   the above vibrations can cause the filling resin 10 to break,        and allow the cooling liquids to infiltrate to the solenoid area        3 and cause a short-circuit.

In view of the above prior art, the object of this invention is toobviate the problems mentioned above with reference to the prior art.

According to the present invention, this object is fulfilled by a platefor a magnetic clamping apparatus as defined in claim 1.

The object is also fulfilled by a process for making a plate for amagnetic clamping apparatus as defined in claim 12.

Finally, the object is also fulfilled by a magnetic clamping apparatusas defined in claim 20.

With the present invention, a one-piece multipole plate can be formedfrom a single piece of ferromagnetic material, thereby affordingconsiderable time savings.

Time savings are also achieved during assembly, because the inventionrequires a single part, i.e. the one-piece multipole plate, to be onlyhandled.

The one-piece multipole plate so obtained allows easy mounting of anumber “N” of pole pieces to the solenoid-reversible magnet unit, nocare having to be taken of the alignment and center-to-center distancebetween the various pole pieces.

Furthermore, with the present invention, the static magnet can beinserted without displacing the pole pieces, no pole piece positionadjustment being required, unlike in prior art apparatus, with the poleplate only having to be centered relative to the frame.

Further advantages of the present one-piece multipole plate may be asfollows:

-   -   when pole extensions are used, their spacing is ensured with        centesimal accuracy, which enhances the accuracy of machining        while using the magnetic apparatus;    -   liquid infiltrations to the solenoid area are prevented, because        the one-piece pole plate creates a metal diaphragm between the        solenoid area and the working surface;    -   the stresses exerted on the plate due to workpiece machining are        arranged all over the plate, which ensures higher vibration        resistance.

Finally, if the inventive plate is used in a dual-magnet magneticapparatus, it can avoid calibration of the two (static and reversible)magnets, because:

1) the pole pieces are arranged with a constant spacing, the pole piecepitch being provided with less than one tenth of a millimeter tolerance;

2) the inventive plate allows partial short-circuiting of any excessmagnetic flux; this can avoid the need of balancing the fluxes of thetwo (static and reversible) magnets, and thus provide time savingsduring assembly.

The characteristics and advantages of the invention will appear from thefollowing detailed description of one practical embodiment, which isillustrated without limitation in the annexed drawings, in which:

FIGS. 1A and 1B are a lateral sectional view of a magnetic apparatus anda plan view of an element of such magnetic apparatus respectively,according to the prior art;

FIG. 2A is a plan view of a first embodiment of the one-piece multipoleplate of the present invention;

FIG. 2B is a lateral sectional view as taken along line X-X of theone-piece multipole plate of FIG. 2A;

FIG. 2C is a plan view of a second embodiment of the one-piece multipoleplate of the present invention;

FIG. 2D is a lateral sectional view as taken along line X′-X′ of theone-piece multipole plate of FIG. 2C;

FIG. 3 shows the plate of FIG. 2A or 2C, when associated with a frame toform a magnetic apparatus of the present invention;

FIG. 4 shows the plate of FIG. 2A or 2C, when associated with a frame toform another magnetic apparatus of the present invention;

FIG. 5A is a plan view of a third embodiment of the one-piece multipoleplate of the present invention;

FIG. 5B is a lateral sectional view as taken along line X″-X″ of theone-piece multipole plate of FIG. 5A;

FIG. 6 shows the plate of FIG. 5A, when associated with a frame to forma magnetic apparatus of the present invention;

FIG. 7A is a plan view of a fourth embodiment of the one-piece multipoleplate of the present invention;

FIG. 7B is a lateral sectional view as taken along line X′″-X′″ of theone-piece multipole plate of FIG. 7A;

FIG. 7C is a plan view of a fifth embodiment of the one-piece multipoleplate of the present invention;

FIG. 7D is a lateral sectional view as taken along line X″″-X″″ of theone-piece multipole plate of FIG. 7A.

Referring to the annexed FIGS. 2A to 7D, in which the elements describedabove are designated by identical reference numerals, a plate for amagnetic clamping apparatus 12 is generally designated by numeral 11.

The plate 11 comprises a plurality of pole pieces 13 which may have, forinstance, a square plan section (FIGS. 2A, 7A), or a circular plansection (FIGS. 2C, 5A, 7C), although more profiles, e.g. triangularprofiles, not shown, may be provided.

The pole pieces 13 extend from the plate 11 and are formed of one piecewith said plate 11, i.e. the plurality of pole pieces 13 are part of theplate.

Thus, the plate 11 is a one-piece multipole plate.

Particularly, a plurality of pole pieces 13 project from the plate 11 todefine the holding surface 12A of the magnetic apparatus 12, on whichthe workpieces to be machined (not shown) may be placed.

Thus, a flat ferromagnetic plate having predetermined width L, length land thickness S is submitted to a number of machining steps to obtainthe plate 11, in which a plurality of pole pieces 13, i.e. six, eight ormore according to special application requirements, are obtained byforming recesses or grooves 15.

More particularly, the grooves 15 define the periphery of each polepiece 13, to form at least one holding area or surface 13A for each polepiece 13.

The holding surface 12A of the magnetic apparatus 12 is defined by thetotality of the holding areas 13A.

It shall be noted that, if the plate 11 is associated with a dual-magnetmagnetic apparatus (with static and reversible magnets), these grooves15 may form a receptacle for the static magnet 9 and the resin 10 (FIGS.3 and 4), and if the plate 11 is associated with a single-magnetmagnetic apparatus (having a reversible magnet only), they may form areceptacle for the resin 10 only (FIG. 6).

The residual material portion of the plate 11 at the grooves 15 definesa connecting portion 11A between the various pole pieces 13, to allowconnections between pairs of pole pieces 13.

Particularly, this portion 11A creates some kind of partialshort-circuit between the static magnets 9 of the pole pieces 13 whenthe magnetic apparatus is activated and can increase the stiffness ofthe pole pieces 13 and hence the plate 11, thereby increasing theresistance of the plate to mechanical stresses.

The overall section of this portion 11A shall preferably but withoutlimitation be less than 30% of the area 13A of each pole piece 13, i.e.shall not exceed 30% of the area defined by the holding surface 13A ofthe pole piece 13.

If the section of the portion 11A is more than 30% the area of theholding surface 13A of each pole piece 13, then the magnetic apparatus12 might exhibit poorer clamping performances.

Still referring to the annexed figures, a through hole 14 can be seenfor each pole piece 14.

This through hole 14 extends through the thickness S of the plate 11(and hence the thickness of the pole pieces 13) and part of thethickness S″ of the portion of the frame 2 that acts as a base for themagnetic apparatus 12.

It shall be noted that the holes 14 may be preferably formed at thecenter C of each pole piece 13.

Regardless of the position of the holes 14, a constant pitch P can beachieved between pairs of centers C.

Advantageously, if the holes 14 are formed at the center C of a polepiece 13, then such holes 14 are aligned along predetermined axes thatare parallel to the axes of a reference system with orthogonal Cartesianaxes X-Y.

It shall be noted that each through hole 14 can have a fastener device17 associated therewith, whose features are described in the Italianpatent application MI2007A001227 that can clamp the solenoid3-reversible magnet 4 unit into a pack between the pole piece 13 and thebase of the frame 2.

The shank of a pole extension (not shown) can be associated with suchfastener device 17.

A description of the technical and operating characteristics of a polarextension, as well as the advantages of the use of a pole extension maybe found, for instance in the Italian Patent IT1222875 and in the PatentApplication MI2007A001353.

Advantageously, while the process for making the magnetic apparatus 12is similar to the one as described above with reference to the prior artof FIG. 1A, it includes a single step during which the plate 11, andhence all the pole pieces 13 can be associated with the frame 2 of theapparatus.

This feature provides considerable time savings both in the pole piecemanufacturing process and, advantageously, during assembly, one piecebeing only handled, and not as many pieces as there are pole pieces 5 tobe mounted to the magnetic apparatus 12.

It shall be noted that, when a pole extension is used, the constructionprocess ensures centesimal accuracy of the center-to-center distancebetween pairs of extensions, which increases workpiece machiningaccuracy.

Particularly referring to FIGS. 2A and 2B, which show a first embodimentof the present invention, six pole pieces 13 are shown to project out ofthe plate 11.

This plate 11, and hence the six pole pieces 13 can be formed from aflat plate by material removal, e.g. through milling or drilling steps.

Particularly, the milling steps define the recesses or grooves 15.

In the particular representation of FIG. 2A, the grooves 15 are formedto extend through at least one depth H of the thickness S of the plate11.

In other words, the thickness S′ of the connecting portion 11A isdefined by the following relation:

S′=S−H

where S is the thickness of the plate 11 and H is the depth of thegrooves 15.

It shall be noted that the grooves 15 of each pole piece of theplurality of pole pieces 13 extend along lines parallel to the axis Xand along lines parallel to the axis Y of a reference system withorthogonal Cartesian axes X-Y, so that the pole pieces 13 have a squareplan shape and are arranged along parallel rows.

The drilling steps form both the through hole 14 and additional throughholes 16 that extend through the section S of the plate 11.

Advantageously, these through holes 16 provide easier alignment of theplate 11 with the frame 2, as well as the passage of resin 10.

Particularly referring to FIGS. 2C and 2D, which show a secondembodiment of the present invention, eight pole pieces 13 are shown toproject out of the plate 11.

Here again, the plate 11 and the eight pole pieces 13 can be formed froma flat plate by material removal, e.g. using a milling machine such as acorer.

Particularly, such milling is carried out concentrically with the centerC of each pole piece 13.

Thus, a plurality of pole pieces 13 with a circular plan section areobtained.

Once again, in the embodiment as shown in these FIGS. 2C and 2D, thethickness S′ of the connecting portion 11A is defined by the relationS′=S−H, where S is the thickness of the plate 11 and H is the depth ofthe grooves 15.

Referring now to FIGS. 3 and 4, there is shown a sectional view of themagnetic apparatus, 12, once the plate 11 as shown in FIG. 2A or 2C hasbeen assembled to the frame 2 of the magnetic apparatus 12.

It can be appreciated from FIGS. 3 and 4 that the plate 11 can serve twotypes of magnetic apparatus 12, such as of the electro-permanentdual-magnet type (having static and reversible magnets) depending on theposition of the plate during assembly.

Particularly, a position known as “front” or traditional position (seeFIG. 4) can be defined, in which the plate 11 as shown in FIG. 2A or 2Cis shown to have a holding surface 12A in which the pole pieces 13 areexposed, and a second position known as “back” or metal position (seeFIG. 3) in which the plate 11 as shown in FIG. 2A or 2C, has a holdingsurface 12A in which the pole pieces will not be visible.

It shall be noted that the apparatus 12 in which the plate 12 is in atraditional position (FIG. 4) provides the advantage of allowing removalof more material from the holding surface 12A of the magnetic apparatus12 because no active part is damaged by the magnetic flux in theinactive condition.

This is particularly advantageous because, due to the deterioration ofthe holding surface caused by machining, the required workpiecemachining accuracy cannot be ensured with time. To obviate thisdrawback, the use of the plate 11 and its placement in accordance withthe pattern as shown in FIG. 4 allow multiple steps to be carried outfor grinding the holding surface 12A of the apparatus 12, whilepreventing any damage to the active part.

On the other hand, the apparatus 12 in which the plate 11 is in a backposition (FIG. 3) provides the advantage of having a much wider metalsurface as compared with the apparatus as shown in FIG. 4 and especiallya resin-free holding surface.

The latter feature is highly advantageous in that the lack of resin onthe holding surface ensures that no failure, deformation and/or peelingoff of resin occurs in case of machining processes that involve anincrease of the temperature of the holding surface 12A.

Furthermore, regardless of which plate position is selected for themagnetic apparatus 12, no liquid can infiltrate to the solenoid area 3,because the one-piece plate 11 creates a metal diaphragm between thesolenoids 3 and the working surface.

It shall be noted that, in the particular case of a dual-magnetapparatus (having static and reversible magnets), the feature of havinga constant distance between the centers C of the pole pieces 13 avoidsthe need for calibration, because partial short-circuiting betweenstatic magnets 9 provided by the portion 11A of the plate 12 makes itunnecessary to perfectly balance the fluxes of the static magnet 9 andthe reversible magnet 4.

It should be further noted that the magnetic apparatus 12 in which theplate 11 has circular pole pieces allows an even better mechanicalstress distribution as compared with the embodiment of FIGS. 2A and 2B,because the residual metal diaphragm is arranged over the wholecircumference of the pole piece 13.

Referring now to FIGS. 5A to 6, which show a third embodiment of thepresent invention differing from the one described with reference toFIGS. 3 and 4, the plate 11 is a special plate for a single-magnetmagnetic apparatus (having a reversible magnet only).

It shall be noted that in the special embodiment as shown in FIG. 5B,the thickness S′ of the connecting portion 11A is defined by thefollowing relation:

S′=S−H−h

where S is the thickness of the plate 11, H is the depth of the grooves15 as measured from a surface 13B opposite the holding surface 13A tothe holding surface 13A, and h is the depth of the grooves 15 asmeasured from the holding surface 13A to the surface 13B opposite theholding surface 13A.

Furthermore, it shall be noted that the holding surface 13A has anannular recess 19 for receiving a ring 19A, preferably made ofnon-magnetic metal material, for concentrating the clamping force ontothe holding surface 13A of the magnetic apparatus 12 when the magneticapparatus is activated.

Referring now to FIGS. 7A-7B and FIGS. 7C-7D, the pole pieces 13 of theplate 11 are obtained by mechanical steps of material removal, i.e. bydrilling the material.

Particularly, these steps involve full material removal from the plate11, to define through grooves 18 with no material therein.

In other words, the through grooves 18 are apertures in which materialhas been removed all through the thickness S of the plate 11, i.e. thedepth H (or h) of the through grooves 18 is equal to the thickness S ofthe plate 11.

These grooves 18 define or form the profile of the pole pieces 13 thatcan assume any shape, e.g. a quadrangular shape (FIGS. 7A and 7B), acircular shape (FIGS. 7C and 7D) or other shapes, such as triangularshapes (not shown).

In other words, the grooves 18 in the plate 11 define the profile of therecesses, each of the latter defining in turn the periphery of the polepieces 13.

Particularly, the grooves 18 may end at the crossing point 18A with apointed-profile to allow connection between the pole pieces 13 andpartial short-circuiting of static magnets (if any) as well as lowermagnetic leakage.

Therefore, along the peripheral edges of the plate 11 and at thecrossing point 18A, connection is allowed between pole pieces 13 forpartially short-circuiting the static magnets as the magnetic apparatus12 is activated.

It shall be noted that, in the embodiment as shown in FIGS. 7A-7B, theareas 18 extend substantially parallel to the axes X, Y of a referencesystem with orthogonal Cartesian axes X-Y.

Conversely, in the embodiment of FIGS. 7C-7D, the areas 18 extendconcentrically with the center C of each pole piece 13.

Those skilled in the art will obviously appreciate that a number ofchanges and variants may be made to the arrangements as describedhereinbefore to meet specific needs, without departure from the scope ofthe invention, as defined in the following claims.

1.-22. (canceled)
 23. A magnetic holding apparatus for holding ferrousworkpieces, comprising a frame (2) adapted to contain a plurality ofpole pieces (13), each of said plurality of pole pieces (13) having aferromagnetic pole member which defines the holding surface part (13A),a solenoid (3) located around a reversible magnet (4) and a plate (11),said plurality of pole pieces (13) extend from said plate (11) and areformed of one piece with said plate (13), wherein said plate (11) isassociated with the frame (2) in a plate position so as to define aholding surface (12A) of said apparatus (12) in which the pole pieces(13) are not visible.
 24. A magnetic holding apparatus as claimed inclaim 23, wherein said plurality of pole pieces (13) are connected witheach other by a connecting portion (11A) of said plate (11), so thatsaid plurality of pole pieces (13) are partially short-circuited duringactivation of said magnetic apparatus.
 25. A magnetic holding apparatusas claimed in claim 23, wherein said plate (11) comprises a plurality ofgrooves (15, 18) which are adapted to define the periphery of each ofsaid plurality of pole pieces (13) and to form said connecting portion(11A) for connection of said plurality of pole pieces (13) to eachother, said plurality of pole pieces (13) have a circular plan section,said grooves (15, 18) being circumferential grooves, whose center (C) isat the center of each pole piece (13).
 26. A magnetic holding apparatusas claimed in claim 23, wherein said plate (11) comprises a plurality ofgrooves (15, 18) which are adapted to define the periphery of each ofsaid plurality of pole pieces (13) and to form said connecting portion(11A) for connection of said plurality of pole pieces (13) to eachother, at least one of said plurality of grooves (15, 18) extendsparallel to an axis (X) of a reference system (X-Y) with orthogonalCartesian axes (X-Y) and at least one second of said plurality ofgrooves (15, 18) extends parallel to another axis (Y) of said referencesystem (X-Y) with orthogonal Cartesian axes (X-Y).
 27. A magneticholding apparatus as claimed in claim 23, wherein each of said pluralityof pole pieces (13) comprises a first through hole (14), said firstthrough hole (14) extending through the thickness (S) of said plate(11).
 28. A magnetic holding apparatus as claimed in claim 27, whereinsaid first through hole (14) has threads for receiving the shank of apole extension.
 29. A magnetic holding apparatus as claimed in claim 24,wherein: each pole piece of said plurality of pole pieces (13) has atleast one face adapted to define a holding surface (13A) and the sectionof said connecting portion (11A) is less than 30% of the area of said atleast one face adapted to define said holding surface (13A).
 30. Amagnetic holding apparatus as claimed in claim 29, wherein saidconnecting portion (11A) has a thickness (S′) equal to the residualdimension between the thickness (S) of the plate (11) and a first depth(H) of said plurality of grooves (15, 18).
 31. A magnetic holdingapparatus as claimed in claim 29, wherein said connecting portion (11A)has a thickness (S′) equal to the residual dimension between thethickness (S) of the plate (11) and said first depth (H) of saidplurality of grooves (15, 18) as measured from a surface (13B) oppositesaid holding surface (13A) to the holding surface (13A) and a seconddepth (h) of said plurality of grooves (15, 18) as measured from saidholding surface (13A) to said surface (13B) opposite said holdingsurface (13A).
 32. A plate (11) for a magnetic clamping apparatus (12),said apparatus (12) having a plurality of pole pieces (13), saidplurality of pole pieces (13) extend from said plate (11) and are formedof one piece with said plate (13) said plate (11) comprises a pluralityof grooves (15, 18) which are adapted to define the periphery of each ofsaid plurality of pole pieces (13) and to form a connecting portion(11A) for connection of said plurality of pole pieces (13) to each otherwherein said plurality of pole pieces have a circular plan section, saidgrooves (15, 18) being circumferential grooves, whose center (C) is atthe center of each pole piece (13).
 33. A plate as claimed in claim 32,wherein each of said plurality of pole pieces (13) comprises a firstthrough hole (14), said first through hole (14) extending through thethickness (S) of said plate (11).
 34. A plate as claimed in claim 33,wherein said first through hole (14) has threads for receiving the shankof a pole extension.
 35. A plate as claimed in claim 32, wherein: eachpole piece of said plurality of pole pieces (13) has at least one faceadapted to define a holding surface (13A) and the section of saidconnecting portion (11A) is less than 30% of the area of said at leastone face adapted to define said holding surface (13A).
 36. A plate asclaimed in claim 32, wherein said connecting portion (11A) has athickness (S′) equal to the residual dimension between the thickness (S)of the plate (11) and a first depth (H) of said plurality of grooves(15, 18).
 37. A plate as claimed in claim 32, wherein said connectingportion (11A) has a thickness (S′) equal to the residual dimensionbetween the thickness (S) of the plate (11) and said first depth (H) ofsaid plurality of grooves (15, 18) as measured from a surface (13B)opposite said holding surface (13A) to the holding surface (13A) and asecond depth (h) of said plurality of grooves (15, 18) as measured fromsaid holding surface (13A) to said surface (13B) opposite said holdingsurface (13A).